1. Field of the Invention
This invention relates to a display device including a display panel.
2. Description of the Related Art
In recent years, plasma display devices having surface-discharge type AC plasma display panels have attracted attention. The plasma display panel is one kind of large, thin color display panels.
Referring to FIG. 1 to FIG. 3 of the accompanying drawings, a conventional surface-discharge AC plasma display panel will be briefly described. FIG. 1 illustrates a portion of the configuration of a conventional surface-discharge AC plasma display panel. FIG. 2 illustrates a cross sectional view taken along the line 2—2 in FIG. 1. FIG. 3 illustrates a cross sectional view taken along the line 3—3 in FIG. 1.
FIG. 2 is first referred to. In a plasma display panel (PDP), discharge is caused in each of pixels between a front glass substrate 21 and rear glass substrate 24 positioned in parallel. The surface of the front glass substrate 21 is the display surface. On the rear-surface side of the front glass substrate 21, a plurality of row electrode pairs (X′,Y′) extend in a longitudinal direction (i.e., the width or horizontal direction) of the display panel. A dielectric layer 22 covers the row electrode pairs (X′,Y′), and a protective layer (MgO) 23 covers the dielectric layer 22. Each row electrode X′, Y′ includes a wide transparent electrode Xa′, Ya′, made from ITO or other transparent conductive film, and a thin (narrow) bus electrode Xb′, Yb′, made from metal film. The electrode Xb′, Yb′ supplements the conductivity of the associated electrode Xa′, Ya′. As best seen in FIG. 1, the row electrodes X′ and Y′ are placed in alternation with discharge gaps g′. The electrodes X′ and Y′ are spaced in the vertical direction (or the height direction) of the display screen. Each row electrode pair (X′,Y′) forms one display line (row or horizontal line) L of the matrix display. The row electrodes X′ and Y′ extend in parallel to each other. As illustrated in FIG. 3, a plurality of column electrodes D′ are provided on the rear glass substrate 24 such that the column electrode D′ extend in the direction orthogonal to the row electrode pairs X′, Y′. Band-shaped barrier walls 25 are formed between the column electrodes D′. The barrier walls 25 are parallel to each other. Fluorescent layer 26 formed from red (R), green (G), and blue (B) fluorescent materials cover the side walls of the barrier walls 25 and the column electrodes D′. Between the protective layer 23 and fluorescent layers 26 exist discharge spaces S′, within which is sealed an Ne—Xe gas containing xenon. In each display line L, discharge spaces S′ are partitioned by the barrier walls 25 at the portions of intersection of column electrodes D′ and row electrode pairs (X′,Y′), to form discharge cells C′ as unit emission areas.
As one method of expressing halftones sequentially to form an image on the surface-discharge AC PDP, the so-called subfield method is employed. Specifically, when display data is N-bit data, the display interval for one field is divided into N subfields such that each subfield emits light a number of times based on a weighting of the corresponding bit in N bits of the display data.
The subfield method is described with reference to FIG. 4. Each subfield comprises a simultaneous reset interval Rc, addressing interval Wc, and sustain interval Ic. In the simultaneous reset interval Rc, reset pulses RPx and RPy are simultaneously applied to the row electrodes X1′ to Xn′ and Y1′ to Yn′ so that reset discharge is induced simultaneously in all discharge cells, and a prescribed amount of wall electric charge is formed within each of the discharge cells. Then, in the addressing interval Wc, a scan pulse SP is applied in succession to the row electrodes Y1′ to Yn′ in each row electrode pair, and display data pulses DP1 to DPn are applied, corresponding to the image display data for each display line, to the column electrodes D1′ to Dm′ to induce address discharge (selective extinction discharge). At this time, all discharge cells are divided, corresponding to the image display data, into emission cells in which the wall charge remains without the occurrence of extinction discharge, and non-emission cells in which extinction discharge occurs and the wall charge is annihilated. Next, in the sustain interval Ic, sustain pulses IPx, IPy are applied to the row electrodes X1′ to Xn′ and Y1′ to Yn′ a number of times corresponding to the subfield weighting. As a result, only discharge cells in which wall charge remains repeat sustain discharge a number of times corresponding to the number of applied sustain pulses IPx, IPy. Due to this sustain discharge, vacuum ultraviolet light of wavelength 147 nm is emitted from the xenon (Xe) sealed within the discharge space S′. This vacuum ultraviolet light excites the red (R), green (G) and blue (B) fluorescent layer formed on the rear substrate so that visible light is emitted, and an image corresponding to the input image signal is obtained.
In the above described image formation in the PDP, the reset discharge is performed prior to the beginning of the address discharge and sustain discharge in order to stabilize the address discharge and sustain discharge. Further, the address discharge is also performed for each subfield. In the conventional PDP, the reset discharge and address discharge are performed within the discharge cells C′ in which visible light is emitted in order to form an image through sustained discharge. Hence light emission appears on the display screen due to reset discharge and address discharge even when expressing black and other dark image colors. This makes the screen brighter and often degrades contrast.